1. Field of the Invention
This invention relates generally to a control system for controlling electronic apparatus and, particularly, to a control system that is adapted to digitally control internal circuitry of video and audio equipment.
2. Description of the Background
Video and audio equipment, such as TV receivers, video tape recorders, and audio tape recorders, that include digital control circuitry are becoming quite prevalent. This kind of digital control circuitry typically employs a microprocessor arrangement and utilizes an internal or inner system bus to facilitate communication between the microprocessor and the various functional blocks of the particular piece of equipment. Generally, when employing the internal bus, a central processing unit (CPU), a read only memory (ROM), and the like are incorporated, which communicate by means of the bus. Operational preset data for each of the various functional circuits is stored in the read only memory and, in normal operation, the preset data is read out from the read only memory under control of the central processing unit. The data so read out from the read only memory is supplied to a predetermined controllable circuit, such as the video processor in a television receiver through the internal bus, so as to permit that particular circuit to perform a predetermined operation. In this approach employing an internal bus, typically each operational system can also be selectively controlled by the central processing unit upon actuation of an external unit, such as a keyboard or remote control unit. The internal bus used in this kind of system can use various communication schemes, such as that disclosed in Japanese patent application No. 57/106262, in which the bus line is a two-wire bus comprised of a data line and a clock line.
In addition, video and audio equipment employing the above-described internal bus system is also advantageously adapted to undergo adjustment procedures during manufacture and maintenance or repair using the control circuitry already in place by connection through a jack or by remote control interface. This permits both standardization of the adjustments of the circuitry, as well as simplification thereof, and leads to overall cost reductions both during manufacture and repair.
Typical of the units employed in a television receiver that may be controlled in such a system are the audio processing circuit, video control circuit, video processor, deflection control circuit, and the tuning circuit. Subsequently, when the television receiver receives control commands fed by the remote control commander or manual keyboard, the central processing unit controls the specific controllable circuit in response to the commands, which might involve tuning, volume adjustment, picture adjustment, and the like.
During the control operation of the various kinds of equipment under discussion here, when the control signals are fed from the main central processing unit to the specific controllable circuits, data representing the control or state contents of the signal are transmitted together with clock signals. In such situation, it has been found that when the clock signal frequency is increased, radio frequency interference due to noise from the clock pulses will appear on the cathode ray tube of the particular piece of apparatus. Accordingly, it is known to avoid such display noise and to transmit data only during the vertical blanking interval of the video signal.
This transmission of data during the vertical blanking interval has lead to the following problem. Because the vertical blanking interval provided for data transmission has only a time interval of 1.17 to 1.33 milliseconds, when data is transmitted in this interval using clock signals having a frequency of 100 kHz, only approximately 117-bytes of data can be transmitted during one vertical blanking interval. Therefore, when 1 byte of data is transmitted with a 1-bit acknowledge bit, then only 13-bytes (117.div.9) can be transmitted.
Therefore, it can be seen that the amount of data that may be transmitted during one vertical blanking interval is severely limited and, thus, the number of communications that can be achieved between the main central processing unit and the various controllable circuits is also limited. Moreover, when the wait time and the like is considered, in some cases the main central processing unit may not be able to check the operational states of all of the controllable circuits within a single vertical blanking interval. In that case, the central processing unit is forced to check the various circuits in the next successive vertical blanking interval and this can result in an unacceptably long response time in the particular piece of equipment.